Skip to content
Login Register

#fluid dynamics

48 public questions tagged with this topic.

Fluid Pressure, Pascal's Law and Manometers

A plate of area 0.07m2 moves at 0.3m/s over a 0.5mm thick water film (η\=1.0×10−3Pa s). What force is required?

Viscous force: F = ηvAl. η = 1.0×10−3Pa s, v = 0.3m/s, A = 0.07m2, l = 0.5×10−3m. F = 1.0×10−3×0.3×0.070.5×10−3 = 1.0×10−3×42 = 0.042N. As per NCERT, applying relevant law/formula with correct units and sign convention leads to 0.042 N. This satisfies dimensional consistency and physical conditions given, so option B is scientifically correct.

Ref: NCERT Class 11 Physics, Thermal Properties and Gravitation.

View Details
Surface Tension, Capillarity and Excess Pressure

A spray tube (10cm2) has 50 holes of diameter 0.9mm. If the flow speed is 2.5m/min, what is the ejection speed?

A1v1 = A2v2, v1 = 2.5m/min = 0.04167m/s, A1 = 10×10−4m2. Hole area: Ah = π(0.45×10−3)2, total A2 = 50×π×2.025×10−7≈3.181×10−5m2. v2 = 10×10−4×0.041673.181×10−5≈1.31m/s. As per NCERT, applying relevant law/formula with correct units and sign convention leads to 1.3 m/s. This satisfies dimensional consistency and physical conditions given, so option B is scientifically correct.

Ref: NCERT Class 11 Physics, Thermal Properties and Gravitation.

View Details
Surface Tension, Capillarity and Excess Pressure

Why does the pressure in a fluid decrease when its speed increases in a horizontal pipe?

Bernoulli’s principle states that in steady flow, an increase in kinetic energy (12ρv2) corresponds to a decrease in pressure energy, as total energy is conserved along a horizontal streamline. As per NCERT, applying relevant law/formula with correct units and sign convention leads to Because of energy conservation. This satisfies dimensional consistency and physical conditions given, so option B is scientifically correct.

Ref: NCBI Bookshelf, Ideal Gas Law: P1V1/T1 = P2V2/T2.

View Details
Surface Tension, Capillarity and Excess Pressure

A spray tube (7cm2) has 35 holes of diameter 0.8mm. If the flow speed is 3.0m/min, what is the ejection speed?

A1v1 = A2v2, v1 = 3.0m/min = 0.05m/s, A1 = 7×10−4m2. Hole area: Ah = π(0.4×10−3)2, total A2 = 35×π×1.6×10−7≈1.759×10−5m2. v2 = 7×10−4×0.051.759×10−5≈1.99m/s. As per NCERT, applying relevant law/formula with correct units and sign convention leads to 2.0 m/s. This satisfies dimensional consistency and physical conditions given, so option B is scientifically correct.

Ref: NCERT Class 11 Physics, Thermal Properties and Gravitation.

View Details
Surface Tension, Capillarity and Excess Pressure

A sphere of radius 0.015m moves at 0.2m/s through water (η\=1.0×10−3Pa s). What is the viscous force?

Stokes’ law: F = 6πηav. η = 1.0×10−3Pa s, a = 0.015m, v = 0.2m/s. F = 6×3.14×1.0×10−3×0.015×0.2 = 5.652×10−5N. As per NCERT, applying relevant law/formula with correct units and sign convention leads to 5.65 × 10⁻⁵ N. This satisfies dimensional consistency and physical conditions given, so option C is scientifically correct.

Ref: NCERT Class 11 Physics, Thermal Properties and Gravitation.

View Details
Surface Tension, Capillarity and Excess Pressure

Why does blowing over a piece of paper lift it upwards?

Bernoulli’s principle states that faster airflow above the paper reduces pressure, while slower air below maintains higher pressure, creating an upward lift due to the pressure difference. As per NCERT, applying relevant law/formula with correct units and sign convention leads to Due to lower pressure above from faster airflow. This satisfies dimensional consistency and physical conditions given, so option C is scientifically correct.

Ref: NCERT Class 11 Physics, Thermal Properties and Gravitation.

View Details
Surface Tension, Capillarity and Excess Pressure

Which statement is incorrect about Bernoulli’s principle?

Bernoulli’s principle assumes non-viscous flow, not high viscosity, as viscosity causes energy loss, violating the energy conservation assumption. The incorrect statement is that it applies to highly viscous fluids. As per NCERT, applying relevant law/formula with correct units and sign convention leads to It applies to highly viscous fluids. This satisfies dimensional consistency and physical conditions given, so option C is scientifically correct.

Ref: NCERT Class 11 Physics, Thermal Properties and Gravitation.

View Details